K.W.J. Barnham

Analysis of nucleon structure functions in CERN bubble chamber neutrino experiments

Abstract We present results for the differential cross sections of neutrinos and antineutrinos on nucleons in the energy range E = 2−200 GeV, from the BEBC and Gargamelle experiments. The structure functions F2, 2χF1 and χF3 have been evaluated as a function of χ and q2. Deviations are observed from Bjorken scaling, which are very similar to those found in electron and muon inelastic scattering. For the Callan-Gross ratio, we find 2χF 1 F 2 = 0.80 ± 0.12 and the corresponding value for 〈R〉 = 〈 σ S σ T 〉 = 0.15 ± 0.10 . Our results are consistent with the Gross-Llewellyn-Smith sum rule; we measure ⩾2.5 ± 0.5 valence quarks per nucleon. Quark and antiquark distributions are given. The Nachtmann moments of F2 and χF3 are quantitatively consistent with the predictions from QCD. The value of the strong interaction parameter is λ = 0.74 ± 0.05 GeV without corrections, and 0.66 ± 0.05 GeV including αS2 corrections. The moments of the gluon distribution are found to be positive and indicate an χ distribution of gluons which is comparable with that of the valence quarks.

Observation of Prompt Neutrinos from 400-GeV Proton Nucleus Collisions

Abstract In 70 000 photos taken in BEBC during an experiment in which the 400 GeV proton beam of the CERN SPS was dumped into a massive Cu target 820 m upstream of BEBC, 70 interactions induced by neutral primaries above 10 GeV were observed. In 11 events the secondary charged lepton is an e − , in four events an e + . This number of electron events cannot be due to electron neutrinos from conventional sources (K, Λ, Σ − decays). The flux of the additional (prompt) neutrinos is evaluated. Possible origins are discussed in terms of charmed particles, τs, and as yet undiscovered particles. Limits are given on axion production.

Search for Heavy Neutrino Decays in the {BEBC} Beam Dump Experiment

Abstract New limits on lepton mixing parameters are derived from a search for decays of heavy neutrinos in a proton beam dump experiment. The limits | U oi | 2 , | U e i | 2 −6 −10 −7 are obtained for neutrino mass eigenstates v i of mass between 0.5 and 1.75 GeV, which can be produced through mixing in charmed D meson decays. This is the first such limit on | U o i | 2 for neutrino masses greater than 0.5 GeV. For the mass eigenstate v 3 in particular, we obtain the limits | U o 3 | 2 −7 −10 −8 , | U e 3 | 2 −9 −10 −10 for the mass range 150–190 MeV, assuming the v 3 to be produced directly in charmed F meson decays.

Hadron production in charged current neutrino and antineutrino interactions at high energy

The general features of hadrons produced in charged current interaction of high-energy neutrinos on nucleons are shown to be basically consistent with the idea of quark fragmentation within the framework of the quark parton model. However, many of the effects observed are shown also to follow from longitudinal phase space. Evidence is presented for a rise in 〈pT2〉 with Q2 in qualitative agreement with the predictions of quantum chromodynamics (QCD).

Total cross sections for charged-current neutrino and antineutrino interactions in BEBC in the energy range 20–200 GeV

Abstract The charged-current cross sections for neutrinos and antineutrinos on nucleons in the energy range 20–200 GeV are given. Taken in conjunction with the previous Gargamelle results, they show that σ E is almost constant with energy for antineutrinos, and falls with energy for neutrinos. The value of 〈q 2 〉 E decreases with energy for both neutrinos and antineutrinos, and these deviations from exact Bjorken scaling are consistent with those observed in electron and muon inelastic scattering. We find no evidence for new heavy quark states with right-handed coupling.

Further study of the prompt neutrino flux from 400 GeV proton-nucleus collisions using BEBC

Abstract In a second beam-dump experiment using BEBC the prompt neutrino flux has been measured and its characteristics studied. The use of targets of variable effective density allowed a determination of the conventional decay neutrino flux and a direct demonstration of a prompt neutrino signal. Assuming that the prompt neutrinos originate in the decay of charmed D mesons then a production cross section is estimated. An upper limit of 10% can be set to the proportion of interactions induced by τ neutrinos.

Total cross sections νμ and ḡnμcharged-current interactions between 20 and 200 GeV

Abstract Exposures of the Ne/H 2 filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ∼ 3100 events with a negative, and ∼ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values σ E between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm 2 (GeV nucleon) −1 , for neutrinos and antineutrinos, respectively. The scaling variable q 2 E decreases significantly with increasing energy both for neutrinos and antineutrinos.

Di-Lepton events in the BEBC narrow-band beam neutrino experiment

Abstract In film taken with BEBC filled with a Ne(74%mol)/H 2 mixture and exposed to the CERN narrow-band neutrino beam (200 GeV), tenμ − μ + , one μ − μ + μ − and five μ − e + events were found in the ν exposure and two μ + μ − events and one μ + e − event in the ν exposure. Assuming the same production mechanism for μμ and μe events, the relative rates, corrected for identification inefficiency and background, can be combined and are (1.3 ± 0.4)% for (μ − e + + μ − μ + )/μ − in neutrino interactions, and (1.2 ± 0.5)% for (μ + e − + μ + μ − )/μ + antineutrino interactions. Eight out of the sixteen μ − l + events have a V 0 , leading to a corrected K 0 -multiplicity of 1.7 ± 0.7. No evidence is found for heavy-lepton production.

The structure of the weak neutral current: An analysis of the hadronic energy distribution from neutrino and antineutrino interactions

Abstract An analysis is presented of the distribution of hadronic energy in neutrino and antineutrino neutral current interactions occurring in BEBC, filled with a neon-hydrogen mixture and exposed to the CERN-SPS narrow-band neutrino beam. This shows that the contributions by scalar or pseudo-scalar forms of the interaction are consistent with zero and pure V, A and V + A are excluded; there is good agreement with the Weinberg-Salam model.

A test of ν stability using a 200 GeV narrow-band neutrino beam at BEBC

Abstract ν e induced events obtained in a 200 GeV narrow-band beam have been studied and compared to the number expected from K e3 + decay. Agreement is found between the expected and observed numbers allowing limits to be set on ν e → ν x mixing.